Hemodialysis machines are utilized by persons having insufficient or inoperative kidney functions. The machines may be used at a health facility or in the patient's home. The machine attaches to the patient through an extracorporeal circuit of blood tubing to a dialyzer having a pair of chambers separated by a thin semi-permeable membrane. The patient's blood is circulated through one of the chambers. The hemodialysis machine maintains a flow of a dialysate through the second chamber. Excess water from the blood is removed by ultrafiltration through the membrane and carried out by the dialysate to a drain.
A typical hemodialysis machine provides a pair of hoses which connect to the dialyzer and include a source of incoming water, a heat exchanger and heater for bringing the water to a required temperature, a source of dialysate concentrate or concentrates which are introduced into the water in a predetermined concentration and necessary pumps, pressure regulators, a deaerator, flow controllers and regulators. In an acetate dialysis system, only one concentrate is utilized, while in the more common bicarbonate dialysis systems, two concentrates, acidified and bicarbonate are utilized.
Bicarbonate dialysis is achieved by sequentially proportioning two concentrates and water into a single dialysate solution. The first mixture consists of water and the Acidified concentrate. For example, when performing Bicarbonate dialysis on a 36.83.times. concentrate basis, the Acidified concentrate contains different amounts of Sodium Chloride, Calcium Chloride, Magnesium Chloride, Potassium Chloride, Acetic Acid, and Dextrose. The nominal volumetric proportioning ratio is 34 parts of water to 1 part Acidified concentrate. The second mixture consists of the Water/Acidified result and the Bicarbonate concentrate. The Bicarbonate concentrate contains different amounts of Sodium Chloride and Sodium Bicarb. The nominal volume proportioning ratio is 19.13 parts Water/Acidified and 1 part Bicarbonate concentrate.
The Bicarbonate and Acidified concentrates are available in many different concentrations to allow a dialysate solution to be tailored for the individual patient. The concentrates are designated by the final concentrations of the chemicals based on the nominal proportioning ratios. In some cases it is desired that the final Sodium and/or Bicarbonate concentration differ from the nominal values. To obtain this, the volumetric mixing ratios are varied from the nominal values.
Acetate dialysis is achieved by the proportioning of a concentrate and water into a single dialysate solution. The nominal proportioning ratio is 34 parts of water to 1 part Acetate concentrate. The Acetate concentrate contains different amounts of Sodium Chloride, Calcium Chloride, Magnesium Chloride, Potassium Chloride, Sodium Acetate, and Dextrose.
The acetate concentrates also are available in many different concentrations again to allow a dialysate solution to be tailored for the individual patient. The concentrates are designated by the final concentrations of its chemicals based on the nominal proportioning ratios. In some cases it is desired that the final Sodium concentration differ from the nominal values. To obtain this, the volumetric mixing ratio is varied from the nominal values.
It is difficult to mix concentrates by volume accurately. This is even more difficult when the ratios are variable such as required in dialysis involving final concentrations that differ from the nominal concentrations. Servo-proportioning utilizing a feedback control based upon a classical proportional-integral control system was developed to achieve the desired concentrations.
Prior art systems, however, have been based upon nominal conductivity values. These nominal conductivity values have been attained from the concentration labels, which concentration values have been found to vary as much as plus or minus five (5) percent by Applicants. If the nominal Sodium (Na) or Bicarbonate (Bicarb) concentrate is to be varied, then the prior art systems again rely on nominal or estimated values, which again can produce errors in the actual final concentrations achieved.